PCs are for spreadsheets, games consoles are for….games 🙂
Any xbox will work fine (although best to get one with a HDD so that you can save your profile, however most do have them).
How fast is your internet connection? It would need to be pretty crap not to run multiplayer.
Yeah, just plug an ethernet cable in the back of your router (or buy an add on wifi connection for the xbox) and you are good to go.
(You’ll need an xbox live subscription to play online, but you normally get a months free with a new game, and Cougar posted a good link for a cheap annual deal, it was about £24 i think)